During oil and gas exploitation a produced fluid containing crude oil and/or natural gas as well as water and other components are obtained from a well. This well stream is transported from the well to a processing site. When the composition, pressure or temperature of the produced fluid changes during transport, then solid hydrates may form. These solids can result in blockage of the pipelines and other equipment. To avoid this problem it is well know to add hydrate inhibitors to the produced fluid. Different types of inhibitors have previously been identified. A well know and often employed inhibitor are glycol based inhibitors such as mono ethylene glycol or other types of glycol with different substituents. Another group of inhibitors are kinetic inhibitors, where the name refers to the ability of the substance to influence the kinetic of the hydrate forming reactions so that these will proceed much slower than what would otherwise be the case.
Conventionally only one type of inhibitor is employed in a particular well stream. The inhibitor is selected based on the composition of the well stream, prevailing conditions and physical requirements.
The glycol based inhibitors have been employed for many years, and systems for separating and regenerating the glycol are also well known. The use of glycol inhibitors is accordingly a proven concept, but the concept also has limitations. For transporting well streams comprising considerable amounts of water and gas over long distances at low temperatures, the concentration of MEG or another glycol based inhibitor needed to avoid hydrate formation increase significantly. This result in the need of relatively large diameter pipelines all the way down to the well to supply the MEG. Increasing the MEG concentration also results in an increase in the total treated well stream to be transported from the well to the processing site.
In these situations it may be economically more attractive to limit the amount of glycol based inhibitor and instead add a kinetic inhibitor which generally needs to be added in small concentrations compared to the glycol based inhibitors to have a sufficient effect. During topside handling of the process fluid for instance prior to depressurization it may however be necessary to introduce additional inhibitor in addition to the kinetic inhibitor. As the distances topside are normally significantly smaller the use of glycol topside as such additional inhibitor is suitable due to its efficiency and well known methods for regeneration and reuse, which limits the need to handle environmental challenging waste streams.
In some cases it is also relevant to combine KHI and lean MEG as a common hydrate inhibitor in the well stream, reducing the necessary feed rates of MEG, and therefore also reducing the size of MEG recovery plant.
The traditional methods for regenerating the glycol based inhibitor for reuse are mainly based on evaporation of water and/or inhibitor and precipitating salts accumulated in the inhibitor stream and removing the solid salt particles. However when employing a kinetic inhibitor combined with the glycol based inhibitor the behavior of the streams, especially the salty glycol stream, changes and it has been identified that the presence of the kinetic inhibitor in the stream may result in formation of agglomerated matter, which again increases the risk of clogging of pipes and other equipment.